Process of purifying metal



Patented Dec. 12, 1933 UNITED STATES PATE PROCESS OF PURIFYING METAL William H. Osborn and mm H. Stout, In, New

York, N. Y., aasignors to coalescence Products Company, Inc., New York, N. Y., a corporation of New York No Drawing. Application August 7, 1981 Serial No. 555,858

6 Claim.

This invention relates to a process for removing impurities from metal particles.

My co-pending application Serial No. 299,665

now Patent No. 1,822,939, issued September 15, 1931 discloses a process for coalescing metals in which separate metal particles are coalesced into a solid homogeneous mass after the surfaces of the particles have been treated to remove impurities that would interfere with the coalescence.

The present invention has for its object an improved method of cleaning the metal particles preparatory to coalescence.

A particular object of the invention is to provide a mixture of gases, in the cleaning of the surfaces of copper particles of combined or adhering impurities, which is reducing to copper oxide but neutral or non-reducing to sulphur dioxide (80:)

Another particular object is to provide a mix- 20 ture of gases, in the cleaning of the surfaces of copper particles of combined or adhering impurities, which is reducing to copper oxide but oxidizing to carbon and carbonaceous material present on the surfaces of the copper particles.

The invention provides a safe and economical method for carrying out these objects.

The invention will be described in detail as applied to the cleaning of electrolytically deposited copper particles, although obviously the same principles can be applied to copper particles produced in other ways, or to particles of other metals, or alloys.

In the electrolytic refining of copper the oathode deposit is made in an electrolyte containing sulphuric acid (H2804) copper sulphate (CllSOO and other metallic salts as impurities.

In withdrawing the cathode from the electrolyte some of it adheres to the copper and leaves on drying some of these metallic salts and other impurities entrained on the surfaces of the oathode crystals.

Much of these entrained impurities may be removed by washing the cathode in hot water or other solvents but within the limits of practical operation it is not possible to do so completely.

Further, on exposure to the air, the surfaces of the cathode crystals become oxidized, the extent of the oxidation depending on length and conditions of exposure.

In using brittle cathodes made by depositing against a copper blank coated with an organic compound from which the deposit is stripped a further impurity results from carbonaceous material of the coating compound adhering to the cathode.

To recapitulate-The impurities found on copper cathode and to which this invention refers are 1. Sulphur from entrained sulphate.

2. Oxygen from exposure to the air and present 00 in the sulphates.

3. carbonaceous material from the coating compound.

4. Arsenic and antimony from the electrolyte which is incidentally partially removed by the as process.

In the coalescence of copper, temperature and pressure are so exerted on a mass of separate copper particles as to cause grain growth to occur across the original particle surfaces. In order 30 that this grain growth shall not be retarded it is necessary that no film or surface of material (such as C1120, C1128, C11S04, etc.) other than pure copper be interposed between the surfaces of the copper particles.

Hence, in coalescing cathode material containing impurities as described above it is necessary at the temperatures at which coalescence takes place, and untfl coalescence is complete, that these impurities shall have been removed from so the particle surfaces.

Our experimentation has disclosed in respect to the elimination of sulphur from cathode copper- First-That for the generalized equation for the dissociation of copper sulphate, viz:

CuSO4+Cu- 2CuzO+S0z which begins at approximately 650 F. and is complete below 1400 F., the S02 gas formed ispo practically non-reactive to copper, i. e., the equation-- SO2+3Hr 2H20+H2S (gas) is very slight at 500 F. but becomes increasingly active with increase of temperature and is marked above 1000 F.

For example, in passing a mixture of equal volumes of SO: and H2 through an externally heated glass tube at 500 F. no S was condensed in the cold portion of the tube, but above 1000 marked condensation of S was observed.

Placing. deoxidized, desulphurized copper particles in the tube treated with the same mixture of gases at 500 F. the copper particles on analysis showed 0.008% S, at 1000 F. 0.03% S and at '1500" F. 0.8% S.

In other words, as the temperature was increased more S0: was reduced to elemental S by the H2 and combined with the copper to form CuzS.

Third.That the equation SO2+2H2S2H20+S being a reversible one the addition of excess steam to the gas mixtures prevented the formation of S as follows:

At 1000 F. the formation of S was completely stopped by addition of E20 vapor to the gas mixture. At 1500 F. the addition of 90% E20 vapor was insuflicient to prevent formation of S. But by using a larger proportion of steam, having less than 1% of hydrogen present in the steam, the formation of S can be prevented below 1600 F.

Fourth-That for the equilibrium equation' at temperatures below 1600 F. the vapor pressure of H25: formed is very slight and a great excess of H2 is required'to desulphurize the copper. Hence, if in the presence of copper, S02 is reduced by Hz to S and combines with the copper to form Cuzs it requires a long time and much excess of H2 to finally eliminate all S.

Fifth-That, CuzS having been formed, water vapor (H2O) present in the current of H2 greatly accelerates removal of S. This is because by the equilibrium reaction:

some S02 is formed and this being substantially unreactive to copper is swept out by the current of gas.

Sixth-That carbon monoxide (CO) reduces S0: to elemental S (for method see above with H2+SO2) but that the reaction is not active before reaching a temperature of 1100" F. and that at 1500 F. the presence of water vapor is suflicient to repress the reduction to S.

Seventh-That the S02 dissociated below the point where its reduction by H: is very active is swept out by a current of Hi: just as by any other carrier gas and that this eifect may account for the elimination of better than 60% of the original S present as sulphates during period of heating to 1600 F. The mixture of steam and hydrogen used in the preferred form of the present invention also acts to sweep away the S02.

Our experimentation has disclosed in respect to the elimination of oxygen from cathode copper-- First-That both H2 and CO will completely deoxidize cathode material at temperatures above 1000 F. but that in passing a current of gas over the surface of oxidized particles the efliciency of reduction is much greater with CO than with Hz.

Second-That pure steam (H30) alone is actions indicated that at 1650 F. only approxiis no longer sufficiently active "to prevent the reoxidation of the metal by traces of steam or oxygen present.

Hence in determining the deoxidation of copper by a current of wet H2 at temperatures over 1000 F. it is necessary to cool in a current of a dry neutral gas such as N2 or else to reduce the flow of H2 and then 0001 so quickly as to submately one part Hz to 76,000 parts of steam was carbon and hydrocarbon residues are completely removed from the surfaces of copper particles.

Second.- That neither dry Hz nor CO would alone remove carbon.

Third.--That in treating brittle cathode which was briquetted or baled. into billet shape the rate at which carbon residue was removed by a current of steam varied inversely with the density of the briquetted billet. For example, a billet briquetted to 83% of the density of solid copper and containing asphalt residue from the embrittling agent to the extent of about .0025% 1 of the weight of the copper was treated for 35 minutes in a current of H20 above 1000 F. up to 1600 F. and showed complete elimination of carbon residue. A billet briquetted' to 92% of the density of solid copper and treated in the same manner required one hour at 1600 F. to effect complete elimination of carbon.

In summarizing our experimentation we found First-That as little as one part hydrogen in 1200 parts water vapor was at temperatures above 1200 F. reducing to copper oxide.

Second.-That SO: gas produced by dissociation of metallic sulphates substantially did not afi'ect copper at the temperatures studied but that it reduced to S or H2S by H: or CO, the S formed did combine with copper to form CuzS and was then hard to remove.

Third.-'Ihat a suflicient excess of steam prevented the reduction of S0: to S by either H: or CO.

Fourth.-That steam was an emcient remover of carbon adhering to the copper particle surfaces.

By combining the results or this experimentation so as to provide most efliciently for removal of dissociated S02, for reduction of oxygen and for elimination of carbon, we found that by treating cathode particles containing slight amounts of hydrocarbon residues in a current of steam containing less than 1 by volume of H2 at elevated temperatures up to 1600 F., substantially complete elimination of 02, S and C were obtained in less than one hour's treatment above 1000 F. This result is due to the fact that this combination of steam and hydrogen is:

(a) Reducing to oxides of copper.

(b) Neutral to S02.

(0) Oxidizing to C. 1

We found that in the case of copper particles briquetted to too great density the reaction between steam and carbon produced within the billet a local concentration of reducing gases sufficiently high to reduce S02 present and hinder 10 or 15%. Changes in the percentages of hydro-v gen and steam may also be made in applying the process to other metals, such as nickel.

We claim: I l. The process of purifying metallic particles which comprises treating the metallic particles at an elevated temperature below the melt point of the metallic particles with a gaseous mixture comprising approximately steam and 15% hydrogen, by volume.

2. The process of purifying metallic particles which comprises treating the metallic particles at an elevated temperature below the melt point. of the metallic particles with a gaseous mixture comprising approximately 99% steam and 1% hydrogen, by volume.

3. The process of purifying copper which comprises treating copper at an elevated temperature below the melt point of copper with a gaseous mixture comprising approximately 85% steam and 15% hydrogen, by volume.

4. The process of purifying copper which comprises treating copper at an elevated temperature below the melt point of copper with a gaseous mixture comprising approximately 99% steam and 1% hydrogen, by volume.

5. The process of purifying metallic particles which comprises treating the metallic particles at an elevated temperature below the melt point of the metallic particles with a gaseous mixture which is reducing to the oxides of the metallic particles, oxidizing to carbon, and neutral to sulphur dioxide, said gaseous mixture consisting of from less than 1% by volume to 15% by volume of hydrogen, the remainder being steam.

6. The process of purifying metallic particles which comprises treating the metallic particles at an elevated temperature below the melt point of the metallic particles with a gaseous mixture whichis reducing to the oxides of the metallic particles, oxidizing to carbon, and neutral to sulphur dioxide, said gaseous mixture consisting of from 85 to 99% by volume of steam and from 15 113 to 1% by volume of hydrogen.

' WILLIAM H, OSBORN.

HARRY H. STOUT, JR. 

